In many industrial applications, it is necessary to move a load for a limited extent in a straight line. Very often a piston-cylinder device in the form of a ram is used for this purpose. One difficulty with using a piston-cylinder device is that, in normal circumstances, the stroke of the piston-cylinder device has to be at least as long as the distance through which the load is to be moved. As soon as the stroke of a piston-cylinder device exceeds about one meter, difficulties arise in supporting the piston rod of the device and the cost of such a device rises rapidly as its length increases. It would be very desirable for a piston-cylinder device to have a stroke of almost indefinite length.